Type 1 diabetes (T1D) occurs as a result of interplay of genetic and environmental factors. Recent genome-wide scans have given much information about the genes that predispose to disease but much less is known of the environmental interaction that causes susceptible individuals to develop T1D. We have recently generated evidence in the Non Obese Diabetic mouse (NOD) that the innate immune response, mediated through the innate immune adaptor MyD88, may plays a critical role influencing development of disease. We showed that mice deficient in MyD88 did not develop diabetes when bred in a Specific Pathogen free (SPF) environment. There was evidence of increased T regulatory cell activity in the pancreatic lymph nodes of these MyD88-/- mice. However, when the mice were rederived into a germ free facility, they developed the same high incidence of diabetes as wild type mice in the same conditions. Re-introduction of a restricted set of gut commensal bacteria (Altered Schaedler's flora) again reduced diabetes. This indicated that the internal commensal environment was influencing the development of disease. Understanding how commensals interact with the internal mucosa to shape our immune system, both innate and adaptive immunity, is critical to explain how chronic inflammatory diseases, including autoimmune diseases, develop. In this project we will 1) investigate the critical time windows for the exposure to intestinal flora in influencing whether disease develops and the associated immune developmental changes; 2) test the importance of expression of MyD88 in intestinal dendritic cells as the most potent antigen presenting cells and the critical link between innate and adaptive immune responses; 3) investigate the importance of expression of MyD88 in intestinal epithelial cells in responding to and sensing the commensal flora. Our studies will enhance our understanding of how the internal environment may shape the immune response and lead to autoimmunity in a genetically susceptible autoimmune diabetes model. In turn, this may help to direct investigation in people genetically susceptible to diabetes and aid development of new strategies for prevention and treatment of type 1 diabetes.